Interfacial Fe-O-Ni-O-Fe Bonding Regulates the Active Ni Sites of Ni-MOFs via Iron Doping and Decorating with FeOOH for Super-Efficient Oxygen Evolution.

The integration of Fe dopant and interfacial FeOOH into Ni-MOFs [Fe-doped-(Ni-MOFs)/FeOOH] to construct Fe-O-Ni-O-Fe bonding is demonstrated and the origin of remarkable electrocatalytic performance of Ni-MOFs is elucidated. X-ray absorption/photoelectron spectroscopy and theoretical calculation results indicate that Fe-O-Ni-O-Fe bonding can facilitate the distorted coordinated structure of the Ni site with a short nickel-oxygen bond and low coordination number, and can promote the redistribution of Ni/Fe charge density to efficiently regulate the adsorption behavior of key intermediates with a near-optimal d-band center. Here the Fe-doped-(Ni-MOFs)/FeOOH with interfacial Fe-O-Ni-O-Fe bonding shows superior catalytic performance for OER with a low overpotential of 210 mV at 15 mA cm-2 and excellent stability with ≈3 % attenuation after a 120 h cycle test. This study provides a novel strategy to design high-performance Ni/Fe-based electrocatalysts for OER in alkaline media.

Surface-Adsorbed Carboxylate Ligands on Layered Double Hydroxides/Metal-Organic Frameworks Promote the Electrocatalytic Oxygen Evolution Reaction.

Metal-organic frameworks (MOFs) with carboxylate ligands as co-catalysts are very efficient for the oxygen evolution reaction (OER). However, the role of local adsorbed carboxylate ligands around the in-situ-transformed metal (oxy)hydroxides during OER is often overlooked. We reveal the extraordinary role and mechanism of surface-adsorbed carboxylate ligands on bi/trimetallic layered double hydroxides (LDHs)/MOFs for OER electrocatalytic activity enhancement. The results of X-ray photoelectron spectroscopy (XPS), synchrotron X-ray absorption spectroscopy, and density functional theory (DFT) calculations show that the carboxylic groups around metal (oxy)hydroxides can efficiently induce interfacial electron redistribution, facilitate an abundant high-valence state of nickel species with a partially distorted octahedral structure, and optimize the d-band center together with the beneficial Gibbs free energy of the intermediate. Furthermore, the results of in situ Raman and FTIR spectra reveal that the surface-adsorbed carboxylate ligands as Lewis base can promote sluggish OER kinetics by accelerating proton transfer and facilitating adsorption, activation, and dissociation of hydroxyl ions (OH- ).

Hierarchical porous Ni, Fe-codoped Co-hydroxide arrays derived from metal-organic-frameworks for enhanced oxygen evolution.

The multi metal organic frameworks (BTC-CoNiFeZn) were used as the precursors of in situ structure reconstruction in alkaline solution, and we synthesized hierarchical porous Ni,Fe-codoped Co-hydroxide nanowire array (Ni0.8Fe0.2/Co-H NAs/NF) catalyst for the oxygen evolution reaction (OER). Benefiting from the rational micro-structure, rich ion-accessible nanopores, and abundant defect sites, the target catalysts possess enhanced intrinsic activity. The obtained Ni0.8Fe0.2/Co-H NAs/NF catalysts show superior OER catalytic activity with a low overpotential of 231 mV at 10 mA cm-2, a small Tafel slope of 32.9 mV dec-1, and high cycle stability for 135 h with performance degradation of only about 4.4%.